1. Field of the Invention
The present invention relates to a novel fluorine-containing elastomer composition. More particularly, the present invention is concerned with a vulcanizable, fluorine-containing elastomer composition which can be used to produce a vulcanization product which has not only excellent resistance to heat, solvents and chemicals, but also improved mechanical properties and compression set resistance. The vulcanizable, fluorine-containing elastomer composition of the present invention can advantageously be used for the production of various articles, such as a fuel hose; a sealant material, such as an O-ring, a seal ring, a packing, a gasket and a diaphragm; a solenoid valve; a needle valve; a blade to be used in a copying machine; a heat-fixing roll; and a valve for industrial uses; and can also be used for the production of composite articles in which the elastomer composition is used in combination with another material or other materials. Especially, the fluorine-containing elastomer of the present invention can most advantageously be used as a material for producing articles which are required to have high resistance to chemicals and solvents, such as fuel hoses, valves and O-rings.
2. Discussion of Related Art
In general, fluorine-containing elastomers have excellent resistance to heat, solvent and chemicals and, therefore, have been widely utilized in the manufacture of sealant materials which are subject to being employed under stringent conditions. Examples of such materials are O-rings, oil seals, packings and gaskets; diaphragm materials and the like.
There are various known methods for vulcanizing a fluorine-containing elastomer, such as a method using a polyamine (the polyamine vulcanization method), a method using a polyol (the polyol vulcanization method) and a method using a peroxide (the peroxide vulcanization method). A suitable vulcanization method is selected according to the intended use of a vulcanization product. Recently, according to the development of a new use, however, with vulcanization products produced by a conventional vulcanization method, such as the polyol vulcanization method, the polyamine vulcanization method and the peroxide vulcanization method, it has become impossible to satisfy various requirements of performance in the new use. Particularly, various problems have been encountered when these conventional vulcanization products are used under stringent conditions (for example, when the products are used in the presence of methanol) or when these products are used in the form of a composite article produced in combination with other types of materials, or when the fluorine-containing elastomer is required to have excellent moldability, such as excellent extrusion processability and mold flow properties.
With respect to the polyamine vulcanization method, the vulcanization product obtained is generally poor not only in strength but also in compression set resistance. On the other hand, the polyol vulcanization method, which is most widely used, is disadvantageous in that the vulcanization product obtained is poor in resistance to solvents, chemicals, especially alkalis, and steam. Further, with any of these two methods, it is difficult to vulcanize a low molecular weight polymer (for example, a polymer having a molecular weight of 50,000 or less).
The peroxide vulcanization method is known to be free from the above-mentioned problems and can be used for producing a vulcanization product having relatively good properties. However, the vulcanization product obtained by the peroxide vulcanization method is poor in metal-adhesion properties and therefore, the vulcanization product is unsuitable for applications in which it is used in combination with metals (such as the use as an oil seal or a valve). Further, in the peroxide vulcanization method, when the fluorine-containing elastomer is brought into contact with air during the vulcanization, the progress of vulcanization is extremely hindered, so that portions of the elastomer are likely to be turn off and left as burrs on the surface of the mold. Furthermore, in the peroxide vulcanization method, it is difficult to vulcanize a high molecular weight polymer, so that the vulcanization product obtained is poor in strength and compression set resistance.
Various proposals were made in order to solve the problems accompanying these vulcanization methods. For example, it was proposed to blend two types of polymers, and then vulcanize the resultant blend using a combination of a polyol vulcanizing agent or a polyamine vulcanizing agent with a peroxide vulcanizing agent (see, for example, Japanese Patent Application Laid-Open Specification Nos. 60-72950, 62-30142 and 62-30143). The polymer blend used in this proposal is a blend of a terpolymer comprising vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and a copolymer comprising tetrafluoroethylene and propylene. However, in this proposal, the rate of the vulcanization reaction is low since the reaction does not involve the formation of such vulcanization sites as formed by deiodination radical reaction or debromination radical reaction On the other hand, a method has been proposed in which a combination of a polyol vulcanizing agent with a peroxide vulcanizing agent is used for vulcanizing a blend of a bromine-containing terpolymer comprising vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and a copolymer comprising tetrafluoroethylene and propylene (see, for example, Japanese Patent Application Laid-Open Specification No. 62-79251). However, in this method, the rate of the vulcanization reaction is low since the bromine atoms, which would form vulcanization sites, are not easily liberated. Further, the vulcanization product obtained by this method is likely to have unsatisfactory properties.
Further, in order to improve adhesion between the fluororubber and NBR (acrylonitrile-butadiene rubber), there has been proposed a laminate material comprising a fluororubber and NBR, wherein the fluororubber has, incorporated therein, a combination of a polyol vulcanizing agent with a peroxide vulcanizing agent (see, for example, Japanese Patent Application Laid-Open Specification No. 61-244545). However, in this laminate material, a conventional fluororubber is used and, therefore, should not be improved in processability, such as roll processability.